linux-kernel - Re: [PATCH v2 2/3] mm, page_owner: decouple freeing stack trace from debug

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Date:   Tue, 01 Oct 2019 08:26:28 -0400
From:   Qian Cai <cai@....pw>
To:     "Kirill A. Shutemov" <kirill@...temov.name>,
        Vlastimil Babka <vbabka@...e.cz>
Cc:     Andrew Morton <akpm@...ux-foundation.org>, linux-mm@...ck.org,
        linux-kernel@...r.kernel.org, kasan-dev@...glegroups.com,
        "Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
        Matthew Wilcox <willy@...radead.org>,
        Mel Gorman <mgorman@...hsingularity.net>,
        Michal Hocko <mhocko@...nel.org>,
        Dmitry Vyukov <dvyukov@...gle.com>,
        Walter Wu <walter-zh.wu@...iatek.com>,
        Andrey Ryabinin <aryabinin@...tuozzo.com>
Subject: Re: [PATCH v2 2/3] mm, page_owner: decouple freeing stack trace
 from debug_pagealloc

On Tue, 2019-10-01 at 14:51 +0300, Kirill A. Shutemov wrote:
> On Tue, Oct 01, 2019 at 10:07:44AM +0200, Vlastimil Babka wrote:
> > On 10/1/19 1:49 AM, Qian Cai wrote:
> > > 
> > > 
> > > > On Sep 30, 2019, at 5:43 PM, Vlastimil Babka <vbabka@...e.cz> wrote:
> > > > 
> > > > Well, my use case is shipping production kernels with CONFIG_PAGE_OWNER
> > > > and CONFIG_DEBUG_PAGEALLOC enabled, and instructing users to boot-time
> > > > enable only for troubleshooting a crash or memory leak, without a need
> > > > to install a debug kernel. Things like static keys and page_ext
> > > > allocations makes this possible without CPU and memory overhead when not
> > > > boot-time enabled. I don't know too much about KASAN internals, but I
> > > > assume it's not possible to use it that way on production kernels yet?
> > > 
> > > In that case, why can’t users just simply enable page_owner=on and
> > > debug_pagealloc=on for troubleshooting? The later makes the kernel
> > > slower, but I am not sure if it is worth optimization by adding a new
> > > parameter. There have already been quite a few MM-related kernel
> > > parameters that could tidy up a bit in the future.
> > 
> > They can do that and it was intention, yes. The extra parameter was
> > requested by Kirill, so I'll defer the answer to him :)
> 
> DEBUG_PAGEALLOC is much more intrusive debug option. Not all architectures
> support it in an efficient way. Some require hibernation.
> 
> I don't see a reason to tie these two option together.

Make sense. How about page_owner=on will have page_owner_free=on by default?
That way we don't need the extra parameter.